Fix double-tap detection in TextView's SelectionModifierCursorController

This restores the logic removed from SelectionModifierCursorController
in ag/9994946. A quick sequence of "tap", "drag", "tap" events (such
as when quickly scrolling a small input field) should *not* be treated
as a double-tap.

Bug: 158948887
Test: Manual and unit tests
  atest FrameworksCoreTests:EditorTouchStateTest
  atest FrameworksCoreTests:EditorCursorDragTest
Change-Id: I9fb9cb06b1e208946566a0f70697c62ee7684ca0